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Kotlin Bytecode Generation

and 

Runtime Performance
Dmitry Jemerov
Dmitry Jemerov, 11-13 May 2016
What is Kotlin
What is Kotlin
What is Kotlin
• Statically typed programming language for JVM, Android and the
browser
• Pragmatic, safe, concise, seamless Java interop
What is Kotlin
• Statically typed programming language for the JVM, Android and
the browser
• Pragmatic, safe, concise, seamless Java interop
Compiling a mixed project
*.java
kotlinc
*.kt
*.class
javac *.class
*.jar
Metadata
@Metadata(

mv = {1, 1, 1},

bv = {1, 0, 0},

k = 1,

d1 = {"u0000"nu0002u0018u0002nu0002u0018u0002nu0002bu0002nu0002u0010bnu0000n
u0002u0010u0002nu0002bu0005nu0002u0018u0002nu0002bu0002bu0017u0018u00002u00020u0001Bu0005¢
u0006u0002u0010u0002Jbu0010u0003u001au00020u0004Hu0007Jbu0010u0005u001au00020u0006Hu0007Jb
u0010u0007u001au00020u0004Hu0007Jbu0010bu001au00020u0004Hu0007J!u0010tu001au0002Hn"u0004b
u0000u0010n2fu0010u000bu001abu0012u0004u0012u0002Hn0fHu0002¢u0006u0002u0010r¨u0006u000e"},

d2 = {"Lorg/jetbrains/LambdaBenchmark;", "Lorg/jetbrains/SizedBenchmark;", "()V", "capturingLambda", "",
"init", "", "mutatingLambda", "noncapturingLambda", "runLambda", "T", "x", "Lkotlin/Function0;", "(Lkotlin/jvm/
functions/Function0;)Ljava/lang/Object;", "production sources for module kotlin-benchmarks"}

)

public class LambdaBenchmark extends SizedBenchmark
{ … }

Working with metadata
class A {

fun foo(): String? = null

fun bar(): String = ""

}



fun main(args: Array<String>) {

println(A::class.functions.filter {

it.returnType.isMarkedNullable

})

}
File-level functions
// Data.kt
fun foo() {

}

public final class DataKt {

public static void foo() {

}

}

@JvmName
@file:JvmName("FooUtils")
fun foo() {

}

public final class FooUtils {

public static final void foo() {

}

}

Primary constructors
class A(val x: Int) {

}

public final class A {

private final int x;



public final int getX() {

return this.x;

}



public A(int x) {

this.x = x;

}

}
Data classes
data class A(val x: Int) {

}

public final class A {
…





public String toString() {

return "A(x=" + this.x + ")";

}



public int hashCode() {

return this.x;

}



public boolean equals(Object o) {
…
}
}

Properties
class A {

var x: String? = null

}

public final class A {

@Nullable

private String x;



@Nullable

public final String getX() {

return this.x;

}



public final void setX(

@Nullable String x) {

this.x = x;

}

}
@JvmField
class A {

@JvmField var x: String? = null

}

public final class A {

@JvmField

@Nullable

public String x;

}
Not-null types
class A {

fun x(s: String) {

println(s)

}
private fun y(s: String) {

println(s)

}

}
public final class A {

public final void x(@NotNull String s) {

Intrinsics.

checkParameterIsNotNull(s, "s");

System.out.println(s);

}



private final void y(String s) {

System.out.println(s);

}

}
Parameter null checks
1 parameter
8 parameters
ns
0 2,25 4,5 6,75 9
Without @NotNull With @NotNull
Extension functions
class A(val i: Int)



fun A.foo(): Int {

return i

}



fun useFoo() {

A(1).foo()

}
public final class ExtFunKt {

public static final void foo(

@NotNull A $receiver) {
return $receiver.getI();

}

}
public static final void useFoo() {

foo(new A(1));

}
Interface methods
interface I {

fun foo(): Int {

return 42

}

}



class C : I {

}
public interface I {

int foo();



public static final class

DefaultImpls {

public static int foo(I $this) {

return 42;

}

}

}

public final class C implements I {

public void foo() {

I.DefaultImpls.foo(this);

}

}
Interface methods: Evolution
interface I {

fun foo(): Int {

return 42

}



fun bar(): Int {

return 239

}

}



// -- separate compilation ——————



class C : I {

}

public interface I {

int foo();
int bar();



public static final class

DefaultImpls { … }

}


// -- separate compilation ——————

public final class C implements I {

public void foo() {

I.DefaultImpls.foo(this);

}

}
Default Arguments
fun foo(x: Int = 42) {
println(x)

}



fun bar() {

foo()

}

public static final void foo(int x) {
System.out.println(x);

}



public static void foo$default(

int x, int mask, …) {


if ((mask & 1) != 0) {

x = 42;

}



foo(x);

}



public static final void bar() {

foo$default(0, 1, …);

}
Default Arguments
1 parameter
8 parameters
ns
0 3,75 7,5 11,25 15
Without default values With default values
@JvmOverloads
@JvmOverloads

fun foo(x: Int = 42) {

}

public static final void foo(int x)
{

}



public static void foo$default(

int x, int mask, …) { … }



public static void foo() {

foo$default(0, 1, …);

}
Lambdas: Functional types
fun <T> runLambda(x: () -> T): T =
x()

private static final
Object runLambda(Function0 x) {

return x.invoke();

}

package kotlin.jvm.functions



/** A function that takes 0 arguments. */

public interface Function0<out R> : Function<R> {

/** Invokes the function. */

public operator fun invoke(): R

}
Lambdas: Noncapturing
var value = 0



fun noncapLambda(): Int 

= runLambda { value }

final class LB$noncapLambda$1 

extends Lambda implements Function0 {



public static final LB$noncapLambda$1 

INSTANCE = new LB$noncapLambda$1();



public final int invoke() {

return LambdaBenchmarkKt.getValue();

}

}
public static int noncapLambda() {

return ((Number)runLambda(

LB$noncapLambda$1.INSTANCE)
).intValue();

}
Lambdas: Capturing
fun capturingLambda(v: Int): Int

= runLambda { v }
public static int

capturingLambda(int value) {

return ((Number)RL.runLambda(

new Function0(0) {

public final int invoke() {

return value;

}

})
).intValue();

Lambdas: Capture and mutate
fun mutatingLambda(): Int {

var x = 0

runLambda { x++ }

return x

}

public static int mutatingLambda()
{

final IntRef x = new IntRef();

x.element = 0;

RL.runLambda(new Function0(0) {

public final int invoke() {

int var1 = x.element++;

return var1;

}

});

return x.element;

}

public static final class IntRef {

public volatile int element;



@Override

public String toString() {

return String.valueOf(element);

}

}
Lambdas
Noncapturing
Capturing
Mutating
ns
0 45 90 135 180
Java Kotlin
Lambdas: inline
fun inlineLambda(x: Int): Int =

run { x }

public static int
inlineLambda(int x) {

return x;

}

/**

* Calls the specified function [block] and returns its result.

*/

public inline fun <R> run(block: () -> R): R = block()
Method References
private fun referenced() = 1



fun runReference() {

runLambda(::referenced)

}

final class MethodReferenceKt$runReference$1 

extends FunctionReference implements Function0
{



public static final MethodReferenceKt
$runReference$1 INSTANCE = new
MethodReferenceKt$runReference$1();



public final int invoke() {

return MethodReferenceKt.access
$referenced();

}



public final KDeclarationContainer 

getOwner() { … }



public final String getName() { … }



public final String getSignature() { … }

}
Loops: Range
fun rangeLoop() {

for (i in 1..10) {

println(i)

}

}

public static final void
rangeLoop() {

int i = 1;

byte var1 = 10;

if(i <= var1) {

while(true) {

System.out.println(i);

if(i == var1) {

break;

}



++i;

}

}

}
Loops: Array
fun arrayLoop(x: Array<String>) {

for (s in x) {

println(s)

}

}
public static void
arrayLoop(@NotNull String[] x) {

for(int var2 = 0; 

var2 < x.length; ++var2) {

String s = x[var2];

System.out.println(s);

}

}

Loops: List
fun listLoop(x: List<String>) {

for (s in x) {

println(s)

}

}
public static final void
listLoop(@NotNull List x) {


Iterator var2 = x.iterator();



while(var2.hasNext()) {

String s =

(String)var2.next();

System.out.println(s);

}

}
Loops
Range
Array
ArrayList
ns
0 27,5 55 82,5 110
Java Kotlin
When: Table lookup
fun tableWhen(x: Int): String =
when(x) {

0 -> "zero"

1 -> "one"

else -> "many"

}
public static String tableWhen(int x)
{
String var10000;

switch(x) {

case 0:

var10000 = "zero";

break;

case 1:

var10000 = "one";

break;

default:

var10000 = "many";

}



return var10000;

}
When: Constants
val ZERO = 0

val ONE = 1



fun constWhen(x: Int): String =
when(x) {

ZERO -> "zero"

ONE -> "one"

else -> "many"

}
public static String constWhen(

int x) {

return x == ZERO ? “zero"
: (x == ONE ? “one" : "many");

}

When: enum
enum class NumberValue {
ZERO, ONE, MANY
}



fun enumWhen(x: NumberValue):
String = when(x) {

NumberValue.ZERO -> "zero"

NumberValue.ONE -> "one"

else -> "many"

}
public static String
enumWhen(@NotNull NumberValue x) {

String var10000;

switch(WhenEnumKt$WhenMappings.
$EnumSwitchMapping$0[x.ordinal()]) {

case 1:

var10000 = "zero";

break;

case 2:

var10000 = "one";

break;

default:

var10000 = "many";

}

return var10000;

}
When
Lookup
Compare
Enum
ns
0 5,5 11 16,5 22
Java Kotlin
Summary
• Kotlin allows writing code which is easy to use from Java
• Performance in most scenarios is on par with Java
• Inline functions 👍
• Measure the performance of your code, not micro-examples
https://www.manning.com/books/kotlin-in-action
Q&A
yole@jetbrains.com
@intelliyole

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Kotlin Bytecode Generation and Runtime Performance

  • 1. Kotlin Bytecode Generation
 and 
 Runtime Performance Dmitry Jemerov Dmitry Jemerov, 11-13 May 2016
  • 4. What is Kotlin • Statically typed programming language for JVM, Android and the browser • Pragmatic, safe, concise, seamless Java interop
  • 5. What is Kotlin • Statically typed programming language for the JVM, Android and the browser • Pragmatic, safe, concise, seamless Java interop
  • 6. Compiling a mixed project *.java kotlinc *.kt *.class javac *.class *.jar
  • 7. Metadata @Metadata(
 mv = {1, 1, 1},
 bv = {1, 0, 0},
 k = 1,
 d1 = {"u0000"nu0002u0018u0002nu0002u0018u0002nu0002bu0002nu0002u0010bnu0000n u0002u0010u0002nu0002bu0005nu0002u0018u0002nu0002bu0002bu0017u0018u00002u00020u0001Bu0005¢ u0006u0002u0010u0002Jbu0010u0003u001au00020u0004Hu0007Jbu0010u0005u001au00020u0006Hu0007Jb u0010u0007u001au00020u0004Hu0007Jbu0010bu001au00020u0004Hu0007J!u0010tu001au0002Hn"u0004b u0000u0010n2fu0010u000bu001abu0012u0004u0012u0002Hn0fHu0002¢u0006u0002u0010r¨u0006u000e"},
 d2 = {"Lorg/jetbrains/LambdaBenchmark;", "Lorg/jetbrains/SizedBenchmark;", "()V", "capturingLambda", "", "init", "", "mutatingLambda", "noncapturingLambda", "runLambda", "T", "x", "Lkotlin/Function0;", "(Lkotlin/jvm/ functions/Function0;)Ljava/lang/Object;", "production sources for module kotlin-benchmarks"}
 )
 public class LambdaBenchmark extends SizedBenchmark { … }

  • 8. Working with metadata class A {
 fun foo(): String? = null
 fun bar(): String = ""
 }
 
 fun main(args: Array<String>) {
 println(A::class.functions.filter {
 it.returnType.isMarkedNullable
 })
 }
  • 9. File-level functions // Data.kt fun foo() {
 }
 public final class DataKt {
 public static void foo() {
 }
 }

  • 10. @JvmName @file:JvmName("FooUtils") fun foo() {
 }
 public final class FooUtils {
 public static final void foo() {
 }
 }

  • 11. Primary constructors class A(val x: Int) {
 }
 public final class A {
 private final int x;
 
 public final int getX() {
 return this.x;
 }
 
 public A(int x) {
 this.x = x;
 }
 }
  • 12. Data classes data class A(val x: Int) {
 }
 public final class A { …
 
 
 public String toString() {
 return "A(x=" + this.x + ")";
 }
 
 public int hashCode() {
 return this.x;
 }
 
 public boolean equals(Object o) { … } }

  • 13. Properties class A {
 var x: String? = null
 }
 public final class A {
 @Nullable
 private String x;
 
 @Nullable
 public final String getX() {
 return this.x;
 }
 
 public final void setX(
 @Nullable String x) {
 this.x = x;
 }
 }
  • 14. @JvmField class A {
 @JvmField var x: String? = null
 }
 public final class A {
 @JvmField
 @Nullable
 public String x;
 }
  • 15. Not-null types class A {
 fun x(s: String) {
 println(s)
 } private fun y(s: String) {
 println(s)
 }
 } public final class A {
 public final void x(@NotNull String s) {
 Intrinsics.
 checkParameterIsNotNull(s, "s");
 System.out.println(s);
 }
 
 private final void y(String s) {
 System.out.println(s);
 }
 }
  • 16. Parameter null checks 1 parameter 8 parameters ns 0 2,25 4,5 6,75 9 Without @NotNull With @NotNull
  • 17. Extension functions class A(val i: Int)
 
 fun A.foo(): Int {
 return i
 }
 
 fun useFoo() {
 A(1).foo()
 } public final class ExtFunKt {
 public static final void foo(
 @NotNull A $receiver) { return $receiver.getI();
 }
 } public static final void useFoo() {
 foo(new A(1));
 }
  • 18. Interface methods interface I {
 fun foo(): Int {
 return 42
 }
 }
 
 class C : I {
 } public interface I {
 int foo();
 
 public static final class
 DefaultImpls {
 public static int foo(I $this) {
 return 42;
 }
 }
 }
 public final class C implements I {
 public void foo() {
 I.DefaultImpls.foo(this);
 }
 }
  • 19. Interface methods: Evolution interface I {
 fun foo(): Int {
 return 42
 }
 
 fun bar(): Int {
 return 239
 }
 }
 
 // -- separate compilation ——————
 
 class C : I {
 }
 public interface I {
 int foo(); int bar();
 
 public static final class
 DefaultImpls { … }
 } 
 // -- separate compilation ——————
 public final class C implements I {
 public void foo() {
 I.DefaultImpls.foo(this);
 }
 }
  • 20. Default Arguments fun foo(x: Int = 42) { println(x)
 }
 
 fun bar() {
 foo()
 }
 public static final void foo(int x) { System.out.println(x);
 }
 
 public static void foo$default(
 int x, int mask, …) { 
 if ((mask & 1) != 0) {
 x = 42;
 }
 
 foo(x);
 }
 
 public static final void bar() {
 foo$default(0, 1, …);
 }
  • 21. Default Arguments 1 parameter 8 parameters ns 0 3,75 7,5 11,25 15 Without default values With default values
  • 22. @JvmOverloads @JvmOverloads
 fun foo(x: Int = 42) {
 }
 public static final void foo(int x) {
 }
 
 public static void foo$default(
 int x, int mask, …) { … }
 
 public static void foo() {
 foo$default(0, 1, …);
 }
  • 23. Lambdas: Functional types fun <T> runLambda(x: () -> T): T = x()
 private static final Object runLambda(Function0 x) {
 return x.invoke();
 }
 package kotlin.jvm.functions
 
 /** A function that takes 0 arguments. */
 public interface Function0<out R> : Function<R> {
 /** Invokes the function. */
 public operator fun invoke(): R
 }
  • 24. Lambdas: Noncapturing var value = 0
 
 fun noncapLambda(): Int 
 = runLambda { value }
 final class LB$noncapLambda$1 
 extends Lambda implements Function0 {
 
 public static final LB$noncapLambda$1 
 INSTANCE = new LB$noncapLambda$1();
 
 public final int invoke() {
 return LambdaBenchmarkKt.getValue();
 }
 } public static int noncapLambda() {
 return ((Number)runLambda(
 LB$noncapLambda$1.INSTANCE) ).intValue();
 }
  • 25. Lambdas: Capturing fun capturingLambda(v: Int): Int
 = runLambda { v } public static int
 capturingLambda(int value) {
 return ((Number)RL.runLambda(
 new Function0(0) {
 public final int invoke() {
 return value;
 }
 }) ).intValue();

  • 26. Lambdas: Capture and mutate fun mutatingLambda(): Int {
 var x = 0
 runLambda { x++ }
 return x
 }
 public static int mutatingLambda() {
 final IntRef x = new IntRef();
 x.element = 0;
 RL.runLambda(new Function0(0) {
 public final int invoke() {
 int var1 = x.element++;
 return var1;
 }
 });
 return x.element;
 }
 public static final class IntRef {
 public volatile int element;
 
 @Override
 public String toString() {
 return String.valueOf(element);
 }
 }
  • 28. Lambdas: inline fun inlineLambda(x: Int): Int =
 run { x }
 public static int inlineLambda(int x) {
 return x;
 }
 /**
 * Calls the specified function [block] and returns its result.
 */
 public inline fun <R> run(block: () -> R): R = block()
  • 29. Method References private fun referenced() = 1
 
 fun runReference() {
 runLambda(::referenced)
 }
 final class MethodReferenceKt$runReference$1 
 extends FunctionReference implements Function0 {
 
 public static final MethodReferenceKt $runReference$1 INSTANCE = new MethodReferenceKt$runReference$1();
 
 public final int invoke() {
 return MethodReferenceKt.access $referenced();
 }
 
 public final KDeclarationContainer 
 getOwner() { … }
 
 public final String getName() { … }
 
 public final String getSignature() { … }
 }
  • 30. Loops: Range fun rangeLoop() {
 for (i in 1..10) {
 println(i)
 }
 }
 public static final void rangeLoop() {
 int i = 1;
 byte var1 = 10;
 if(i <= var1) {
 while(true) {
 System.out.println(i);
 if(i == var1) {
 break;
 }
 
 ++i;
 }
 }
 }
  • 31. Loops: Array fun arrayLoop(x: Array<String>) {
 for (s in x) {
 println(s)
 }
 } public static void arrayLoop(@NotNull String[] x) {
 for(int var2 = 0; 
 var2 < x.length; ++var2) {
 String s = x[var2];
 System.out.println(s);
 }
 }

  • 32. Loops: List fun listLoop(x: List<String>) {
 for (s in x) {
 println(s)
 }
 } public static final void listLoop(@NotNull List x) { 
 Iterator var2 = x.iterator();
 
 while(var2.hasNext()) {
 String s =
 (String)var2.next();
 System.out.println(s);
 }
 }
  • 34. When: Table lookup fun tableWhen(x: Int): String = when(x) {
 0 -> "zero"
 1 -> "one"
 else -> "many"
 } public static String tableWhen(int x) { String var10000;
 switch(x) {
 case 0:
 var10000 = "zero";
 break;
 case 1:
 var10000 = "one";
 break;
 default:
 var10000 = "many";
 }
 
 return var10000;
 }
  • 35. When: Constants val ZERO = 0
 val ONE = 1
 
 fun constWhen(x: Int): String = when(x) {
 ZERO -> "zero"
 ONE -> "one"
 else -> "many"
 } public static String constWhen(
 int x) {
 return x == ZERO ? “zero" : (x == ONE ? “one" : "many");
 }

  • 36. When: enum enum class NumberValue { ZERO, ONE, MANY }
 
 fun enumWhen(x: NumberValue): String = when(x) {
 NumberValue.ZERO -> "zero"
 NumberValue.ONE -> "one"
 else -> "many"
 } public static String enumWhen(@NotNull NumberValue x) {
 String var10000;
 switch(WhenEnumKt$WhenMappings. $EnumSwitchMapping$0[x.ordinal()]) {
 case 1:
 var10000 = "zero";
 break;
 case 2:
 var10000 = "one";
 break;
 default:
 var10000 = "many";
 }
 return var10000;
 }
  • 38. Summary • Kotlin allows writing code which is easy to use from Java • Performance in most scenarios is on par with Java • Inline functions 👍 • Measure the performance of your code, not micro-examples